It also comes with a built-in rechargeable battery receiver that can be charged in AC/DC output for saving over replaceable batteries. Sony - 900 MHz Nursery Monitor and Dual Receiver: * Sony nursery monitor receiver has five sound-sensor activity lights, out-of-range indicator and low-battery warning keep you informed of your baby"s actions and the status of your equipment * A belt-clip is included for both receivers, keeping your hands free for other activities * Receivers are water-resistant for use in the bathroom or kitchen * 900 MHz technology: extends the range to let you take the receivers farther from the nursery, yet still hear activities in the nursery * 27 channels to greatly minimize interference: uses FM transmission system with channel selector to locate the clearest channel, helping to eliminate interference for clearer communication * Sony Nursery Baby Monitor and Dual Receiver has a built-in rechargeable battery receiver: provides great savings and convenience over replaceable batteries * Voice activation mode: eliminates most extraneous background noise for clearer transmission * Out of range indicator: beeps and lights up when unit is out of range * AC/DC operation: operates on standard household current or supplied rechargeable batteries